The present invention relates to a light beam scanning device which is employed in an optical image reading system in which a laser light beam is deflected by an optical deflector to scan an original document and to read the data of the original utilizing photoelectric conversion or an image recording system in which an image is reproduced or various data is recorded by scanning a surface of a recording material with a laser light beam.
In general, it is required that a scanning light beam be deflected at a constant speed along scanning lines such as is required to form an original image on a recording surface. In order to satisfy this requirement, a technique using an F.multidot..theta. lens or a parabolic mirror has been proposed in the art as disclosed in the Proceeding of the 8th Display Engineering Conference, pages 101 to 104 in a paper entitled "The Fundamental Problems of Scanning Optical System in Laser Recording and Optical Techniques" (presented on Nov. 18, 1977), Japanese Laid Open Patent Application No. 41149/1979 entitled "F.multidot..theta. Lens", and Japanese Laid Open Patent Application No. 113751/1977 entitled "Light Scanning Device". Furthermore an open-loop control technique has been proposed in which, as disclosed in the specification of Japanese Patent Application No. 147027/1977, a non-linear signal is applied to an optical deflector which has been corrected in advance so that a light beam is scanned at a uniform speed over an image or recording surface.
Unfortunately, the first-mentioned technique is disadvantageous in that an F.multidot..theta. lens or parabolic mirror is much more expensive than an ordinary photographing lens or a plane mirror. The second-mentioned technique is also disadvantageous in that a circuit for generating the shaped non-linear signal is rather intricate and that the accuracy of the signal is low because no correction can be made for various variational factors such as electrical drift because of the open loop configuration.
Accordingly, an object of the present invention is to provide a light beam scanning device which is simple in construction, low in manufacturing cost and high in accuracy and yet can scan a light beam at a uniform speed.